These efforts cover both basic and applied aspects of mycoplasmas and related wall-free prokaryotes, including their neurotoxins, antigens, biologic or genetic factors involved in virulence, immunological interrelationships, and possible role in human disease or diseases of uncertain etiology. Current efforts are directed to the characterization of a newly recovered mycoplasma from the urogenital tract of patients with non-gonococcal urethritis. The unique terminal structure on the organism appears to be involved in attachment of the microbe to erythrocytes, tissue cells, and other surfaces. Pathogenicity studies, utilizing experimental inoculation of organisms into the urogenital tract of a variety of primates, indicates the new mycoplasma can colonize primate for periods of at least 8-9 weeks. Efforts to characterize the pathogenicity and serological properties of an expanding group of helical mycoplasmas (spiroplasmas) have continued. Experimental brain infection of suckling rats (with the GT-48 strain of Spiroplasma mirum) yielded correlation between the histopathological changes, numbers of viable organisms in brain tissue, and immunocytochemical localization of spiroplasmas. Infection of the gray matter of brain supports our concept that the spiroplasmas induce responses similar to other slow degenerative brain diseases of man.